This application relates to measurements of surface slopes and other topological properties of surfaces in flat panels, substrates, and wafers, and more particularly, to optical techniques and systems for such measurements.
Optical interference occurs when two or more optical beams that are at least partially coherent spatially overlap with one another. Various optical interferometers use interference of two coherent optical beams to produce an interference pattern of interference fringes caused by the differences in optical path lengths of the two interfering optical beams. One application of such interference is to extract information embedded in at least one of the interfering beams in the optical measurements and to characterize properties of surfaces under investigation such as surface topographical properties.